Pneumatic Butterfly Valve

What is a pneumatic butterfly valve? 

This is a butterfly valve that operates using a pneumatic actuator. A pneumatic butterfly valve uses compressed air to open and close the valve. These valves are under the category of quarter turn valves. As such, the valve disc makes a quarter turn angle to start or stop fluid flow. Pneumatic butterfly valve manufacturers design this valve with different materials which makes such valves suitable for use in various applications. Pneumatic butterfly valve manufacturer makes the valve such that the disc remains in the flow path when the valve is open or when it is closed. Such a mechanism contributes to pressure drop which then reduces efficiency. However, these valves are small in size, compact and simple in design. Such design makes butterfly valves with a pneumatic actuator cheaper compared to other valves. The design also helps these valves to work in slurries and sludge applications as the disc can hardly get clogged. 

Figure: Pneumatic butterfly valve.

Components of a pneumatic butterfly valve 

Body 

The body is the part that holds all the other parts of a pneumatic butterfly valve. The body is made of very strong metallic materials like carbon steel and stainless steel to ensure high strength. However, there are special category of these valves that are made of wholly plastic materials. The body contains holes to hold bolts used to connect the valve to the pipe. 

Pneumatic actuator 

This is the part that provides the torque used to open and close the valve. The actuator is connected to the valve disc via the stem. When the actuator turns the stem, the disc turns simultaneously allowing or blocking fluid flow. 

Stem

This is the part of a pneumatic butterfly valve that connects the valve disc and the actuator. The stem helps to transmit torque from the actuator to the disc to make the valve open or closed. 

Disc 

This is the component of a pneumatic butterfly valve that is responsible for starting and stopping fluid flow. 

Seat 

This component helps to prevent fluid leakage when the valve is closed. The seat serves to provide a surface where the disc seats when the valve closes. 

Gasket 

This is a component placed between the pipe and valve mating surfaces to prevent fluid leakage between the connections. The gasket is made of different materials depending on working temperature and type of fluid. 

Figure: Components of a pneumatic butterfly valve.

How does a butterfly valve with pneumatic actuator work? 

A pneumatic butterfly valve operates by making a quarter turn to either open or close. The ability to open or close is enhanced by a pneumatic actuator that produces power in terms of torque that twists the disc to open and close. To start a pneumatic butterfly valve, the actuator is turned on. The powered actuator produces torque and transmits it to the disc via the stem. This makes both the stem and disc rotate in the anticlockwise direction. This rotation of the disc makes the valve open allowing fluid to flow through the valve. In this closed state, the disc is oriented parallel to the fluid flow. To close the valve, the actuator turns the stem and disc in the clockwise direction. This rotation makes the disc perpendicular to the fluid flow direction and thus blocks any attempt of the fluid to cross the valve. Pneumatic butterfly valve manufacturers design these valves for use in throttling applications. 

Figure: Working of a pneumatic butterfly valve.

Types of pneumatic butterfly valves 

Concentric butterfly valve with pneumatic actuator 

This is a pneumatic butterfly valve also referred to as a zero offset pneumatic butterfly valve. This is the most basic design. The valve stem is designed to pass through the center of the disc which is placed at the center of the pipe bore. The seat is placed in the diameter periphery of the body. Pneumatic butterfly valve manufacturers use resilient seats or rubber seats to make these valves. This makes the valve very efficient in ensuring zero fluid flow when fluid flow is closed. However, this valve can only be used in applications where the operating temperature is below 60^o degrees as high temperatures can damage the valve seat. Concentric butterfly valve with pneumatic actuator have the advantage that media goes through the valve without contacting the body because the seat is made like a cartridge or sleeve inside the valve body. 

Figure: Concentric butterfly valve with pneumatic actuator.

Eccentric butterfly valve with pneumatic actuator 

This is a pneumatic butterfly valve in which the stem is offset from the center-line of the valve disc. A valve designed with the stem behind the center of the disc is known as a single-offset butterfly valve. Pneumatic butterfly valve manufacturers design this valve to help reduce contact between the seal and disc before the valve is fully closed which helps to improve the lifespan of the valve. 

Other versions of this valve are the double offset and triple offset. A double-offset pneumatic butterfly valve is designed with the stem behind the disc and an extra offset on one side. With double eccentricity, the stem can rotate the disc to rub over the valve seat for around 1^o to 3^o degrees. A triple offset pneumatic butterfly valve is meant for use in critical applications. Pneumatic butterfly valve manufacturers design this valve similar to the double version but this one has one more offset. This third offset is made by the axis of disc and seat contact. Pneumatic butterfly valve manufacturers design this triple off-set valve with metallic seats to enhance tight shut-off free from any leakage as well as make the valve suitable for use in high temperatures. This valve is also very efficient and it is not prone to wear. 

Figure: Eccentric butterfly valve with pneumatic actuator.

Wafer butterfly valve with pneumatic actuator 

This is the most economical of the pneumatic butterfly valves. This is a pneumatic butterfly valve that is placed between two pipe flanges. Bolts are used to connect the valve. The bolts used are long enough to cross the valve body. Also, pneumatic butterfly valve manufacturers design the body with short lengths making it economical to connect and also light in weight. The connection between the valve and the pipe is made tight by using gaskets or O-rings. These seals are placed between the mating surfaces of the valve and the pipe. 

Figure: Wafer butterfly valve with pneumatic actuator

Lug butterfly valve with pneumatic actuator 

This is a pneumatic butterfly valve designed with threaded lugs around the body. The threaded lugs are meant to hold bolts used to connect the valve and pipe together. Two sets of bolts are used to secure the valve and pipe. This type of valve makes it easier to disconnect the valve without affecting the other side of the pipe. Once the valve and pipe are connected, the valve body carries the weight of the pipe unlike in the wafer-type valve. 

Figure: Lug butterfly valve with pneumatic actuator.

Double flange pneumatic butterfly valve 

This is a pneumatic butterfly valve designed with flanged ends on both sides of the ports. This helps to connect the valve to the pipe using bolts. Pneumatic butterfly valve manufacturers design this type of valve with double flanges to make installation easier and more precise. This valve has the advantage of being adaptable to lined pipes since the disc protrusion past the body length is negligible. Pneumatic butterfly valve manufacturers recommend this valve for use in high-pressure applications due to the high strength accorded by bolts, nuts, and flanges. The valve can also be used in high and low temperatures depending on the materials used to make seals and seats. 

Figure: Double flange butterfly valve with pneumatic actuator.

Plastic pneumatic butterfly valve 

This is a special type of pneumatic butterfly valve that is made of plastic material. Pneumatic butterfly valve manufacturers use plastic materials that have high strength like polyvinyl chloride and propylene. This type of valve is cheaper compared to other types of butterfly valves with a pneumatic actuator. The low cost arises from the low cost of plastic materials as well as less amount of energy needed in forming the valve relative to that needed in making metallic valves. Plastic pneumatic butterfly valves are also very light in weight compared to the metallic types. The working principle of these valves is the same as other butterfly valves with a pneumatic actuator. Plastic pneumatic butterfly valves have excellent corrosion resistance compared to their metallic counterparts. The only challenge with these valves is that they cannot work in high temperatures since the plastic material would melt down and thus destroy the whole valve. As such, pneumatic butterfly valve manufacturers recommend the use of these valves in low temperatures that is below 60 ^oC.

Figure: Plastic pneumatic butterfly valve.

Applications of pneumatic butterfly valves 

• Foods and beverages industries. 
• Pharmaceutical manufacturing industries. 
• They are used by different chemical manufacturers.
• These valves are used in steam applications. 
• Pneumatic butterfly valves are used in firefighting applications. 
• They are used in the oil and gas industries. 
• These valves are used in water purification and treatment applications. 
• They are used in slurries and sludge applications.
• Butterfly valves with pneumatic actuators are used in the paper and pulp manufacturing industries. 

Advantages of pneumatic butterfly valves 

• These valves can operate in both low and high torque applications. 
• Operate very fast.
• Less expensive compared to other valves.
• These valves are small in size and light in weight. 
• Simple and compact design leading to high strength. 
• They occupy a small area when installed compared to other valves. 
• They have a low-pressure loss and thus high efficiency. 
• They are durable if used according to the pneumatic butterfly valve manufacturer’s instructions. 

Disadvantages of pneumatic butterfly valves 

• These valves are expensive compared to the manual types. 
• The closure and opening of the valve disc are affected by fluid turbulence and thus tend to reduced efficiency. 
• These valves cannot provide an excellent fluid seal compared to other valves like ball valves. 

Troubleshooting pneumatic butterfly valves 

Internal fluid leakage 

• The valve seat is damaged or worn out. Replace the valve seat. 
• The valve disc is damaged. Replace the disc. 
• O-rings are damaged or worn out. Replace the O-rings. 
• Foreign materials in the valve. Open the valve and remove any foreign materials. 

External fluid leakage 

• The gasket is damaged or worn out. Replace the gasket. 
• Worn-out O-rings. Replace the O-rings. 
• Loose connection. Tighten the bolts to attain the torque recommended by the pneumatic butterfly valve manufacturers. 

Valve does not start

• No power supply in the actuator. Check the availability of power from the source and correct if there is any malfunction. 
• Blockage in the valve. Open the valve and remove any material causing a blockage. 

Summary 

Pneumatic butterfly valves operate using a pneumatic actuator. The actuator is assembled on top of the valve. The pneumatic actuator provides the torque used to turn the stem to open and close the valve. Butterfly valves with pneumatic actuator open by turning the disc for a quarter turn which allows the disc to rotate leaving the fluid flow passage unobstructed. To close the valve, the actuator turns the disc for another quarter turn in the opposite direction. This makes the disc perpendicular to the fluid flow direction hence no fluid can cross the valve.